1. Field of the Invention
The present invention relates to an integrated circuit wafer processing system and more, particularly, to a multiple chamber wafer processing system that utilizes an automatic cleaning feature which alleviates delays in the process sequence.
2. Description of the Background Art
A multiple chamber integrated circuit processing system which is capable of performing multiple processes sequentially and simultaneously on workpieces, such as integrated circuit wafers, is shown in U.S. Pat. No. 4,951,600 issued to Maydan, et al. (Maydan I) and U.S. Pat. No. 5,292,393 also issued to Maydan, et al. (Maydan II), the disclosures of which are incorporated herein by reference.
The multiple chamber processing system described in Maydan I and Maydan II are basically an integrated vacuum processing system that includes one or more load lock chambers, a transfer chamber and a plurality of vacuum processing chambers communicating with the load lock and transfer chambers through selectively closeable slit valves in each chamber. Each of the processing chambers can be adapted to perform one or more integrated circuit processes such as chemical vapor deposition, physical vapor deposition and rapid thermal processing of one or more wafers positioned within the chamber.
The chemical process regulation and control of the elements of the multiple chamber processing system is provided by a real time multi-tasking control program which permits interactive user input and supervision. In general, a sequencer task module reads a wafer order list which contains the identification and processing recipe, or sequence, for each wafer and schedules the transfer of the wafers among the processing chambers and the process chemistries which occur therein.
The processing chambers after a certain period of time become contaminated from the processing chemicals and must be cleaned. This period is relatively variable because it is dependent upon a number of parameters which generally describe the number and type of process the chamber has used. Process chambers which utilize some chemistries, particularly corrosive ones, ones that have a probability of contaminating subsequent chemistries, or those process chemistries which are inclusive to all wafers, generally require cleaning more often. A particular sequence of chemistries may cause the process chambers to become contaminated quicker and cleaning must take place at what may seem to be random intervals.
In the past, the time needed for cleaning of a chamber was measured outside the real time process sequence by a user and when an alarm was triggered indicating that a certain time has passed or at periodic intervals, the entire system was shut down and the cleaning process was performed. This meant the operator needed to understand what process chemistries had occurred prior to that time, how many and in what order. The operator would then select from a matching cleaning list to perform a number of cleaning recipes on that chamber before restarting the automatic process sequence.
This prior cleaning procedure is quite slow and causes the throughput of the multi-chamber processing system to suffer substantially. The system does no processing while the cleaning process is being effected and the system needs to be pumped down to vacuum after the cleaning process has been completed. Further, with additional process chambers and more complicated sequential processes, it is very difficult for the operator to initiate the correct cleaning recipes at the proper time and still maintain an optimum throughput. This causes additional delays while the operator is determining the recipe to use from the historic data of the processes used and the prior cleaning interval. Additionally, there is still some probability of an operator making an error in choosing a cleaning process which could affect subsequent wafer processing and the quality of the product.
Therefore, a need exists in the art for a automatic cleaning sequence which can be fully integrated with the process chemistry recipes and the automatic manufacturing sequence. One particularly advantageous candidate for an automatic cleaning process is termed a xe2x80x9cdry cleaningxe2x80x9d process which uses cleaning agents in a gaseous state and heat to clean the process chambers instead of wet chemicals. Such dry cleaning steps are able to be regulated under computer control and can be accomplished while a process chamber is off-line and the rest of the manufacturing sequencing is being completed normally.
The invention provides a multiple chamber processing system with a multi-tasking sequencer control which performs an automatic dry cleaning process for the process chambers of the system. The cleaning process is accomplished in combination with the manufacturing process which allows the system to continue to process workpieces of the integrated circuit wafer type while a particular one of the process chambers is being cleaned.
The dry cleaning process is automatically scheduled to be seamless with the processing schedules of workpieces in the system. The dry cleaning of a process chamber can then take place at the same time another process is occurring in an adjacent process chamber. The integration of the automatic cleaning process as a system process eliminates the substantial down time which was formerly used for stopping all of the processes when a process chamber was due for cleaning. Workpieces are automatically scheduled around the busy process chamber as they would be when another wafer was being processed. This allows the manufacturing process to be truly continuous and increases throughput significantly.
The dry cleaning processes are performed according to recipes. These recipes correspond to the process chemistries used in a process chamber that is to be cleaned. The cleaning recipe for a particular chamber is thereby formulated on the basis of actual use of the chamber so that it: (1) may be cleaned efficiently when it needs to be and no other process steps for other wafers are contaminated from the residual chemistries in the chamber and (2) process chambers are not cleaned unnecessarily when there is no need to clean a process chamber which saves system resources and increases overall utilization of the system.
The cleaning process is individualized for each process chamber and may be called on a time of usage basis, in the preferred implementation, the number of wafers processed in the process chamber or the accumulated RF on time for the heating elements of the process chamber. Alternatively, the individualized cleaning process may be called because of a change in the type of wafer processed by noting the end of a particular lot processed through the chamber.
In the illustrated implementation of the invention, these methods are executed by a process control sequencer which controls a multiple chamber processing system including one or more load lock chambers, a buffer chamber, an orientor chamber, and a plurality of vacuum processing chambers. Each of the process chambers is adapted to perform one or more integrated circuit processes on the workpieces. A wafer transfer mechanism located centrally in a transfer chamber is used to move wafers among the specialized chambers and process chambers during the process sequence.
The process control sequencer is part of a multi-tasking control program which includes several real time modules including modules for the control of processes within the process chambers and for the transfer of wafers to and from the process chambers. The process sequencer acts on a wafer order list that identifies the wafers of a particular lot of wafers and the operations which they are to be subjected, i.e., their process recipes. The wafers are transferred from chamber to chamber by matching the chemistry steps in the process recipe with the capabilities of the process chambers by commands from the process control sequences to a chamber task module which actually controls the wafer transfer mechanism. The wafer transfers are ordered according to a wafer move list which identifies the workpieces needed to be moved and the sequence for their transfer.
The wafer order list indicates the process recipe to be used for the particular wafer. Preferably, each process recipe program contains a header section which indicates a corresponding cleaning sequence and the criteria for calling the cleaning sequence based on actual usage. The cleaning sequence is comprised of a number of cleaning recipe programs or routines assembled on the basis of the chemistries of an associated process recipe program. Off line editors for formulating the process recipe programs and the cleaning recipe programs in tandem are provided by the process control.
Alternatively, a stored cleaning sequence may be called by an operator if there is not a preprogrammed sequence in a process recipe. This feature allows the automatic cleaning of a process chamber to be scheduled by the process control for specialized processes for which cleaning processes have not been programmed.